SAN DIEGO – Administering inpatient antiviral influenza treatment may reduce admissions to the ICU among adults hospitalized with flu, according to a study presented at ID Week 2017, an infectious diseases meeting.

While interventions did not directly affect flu-related deaths, lower ICU admission rates could reduce morbidity as well as ease the financial burden felt during the influenza season.

Investigators retrospectively studied 4,679 influenza patients admitted to Canadian Immunization Research Network Serious Outcomes Surveillance (SOS) Network hospitals during 2011-2014. Of the 54% of patients given inpatient antiviral treatment, the risk of being admitted to the ICU was reduced by 90% (odds ratio, 0.10;95% confidence interval, 0.08-0.13; P less than .001).

Antiviral treatment was not protective against death outcomes in patients with either influenza A or influenza B (OR, 0.9; 95% CI, 0.7-1.2; P =.454).

The median age of patients was 70 years, with a majority older than 75 years(41%); the majority presented with one or more comorbidities (89%), and had influenza A (72%).

Researchers found that, of the 4,679 patients studied, 798 (16%) were admitted to the ICU, 511 (11%) required mechanical ventilation, and the average length of hospital stay was 11 days.

Of those studied, 444 (9%) died within 30 days of discharge.

Researchers also found that only 38% of those studied had received the current seasonal vaccine upon admittance. However, these numbers may be skewed from the general population, because patients who have not taken the vaccine are more likely to be hospitalized.

Along with the results of antivirals on hospitalized patients, researchers wanted to uncover how the effectiveness of inpatient vaccine administration would vary based on treatment timing, said presenter Zach Shaffelburg of the Canadian Center for Vaccinology, Dalhousie University, Halifax, NS.

Even when administered 4.28 days after symptom onset, antiviral treatments in patients proved to be associated with significant reductions in ICU admissions and the need for mechanical ventilation.

The investigators concluded that antivirals show a strong association with positive effects on serious, influenza-related outcomes in hospitalized patients and, while therapy remained effective with later treatment start, patients would benefit the most from initiation as soon as possible.

Currently, the U.S. Centers for Disease Control and Prevention and the Canadian Immunization Research Network (CIRN) have guidelines instructing best practice for inpatient antiviral treatment, however the number of hospitalized patients given treatment has declined in Canada since 2009, according to Mr. Shaffelburg.

The reason more patients were not receiving inpatient antiviral treatment may be related to studies of different populations that failed to show significant impact, Mr. Shaffelburg suggested during a question and answer session following the presentation: “I think a lot of that comes from outpatient studies that involve patients who are younger and quite healthy [who received] antivirals, and it showed a very minimal impact,” Mr. Shaffelburg said. “So a lot of people saw that study and thought, ‘What’s that point of giving it if it’s not going to make an impact?’ ”

Mr. Shaffelburg and his colleagues are planning to continue their study of inpatient antiviral treatment, focusing more on the effectiveness of treatment in relation to time administered after onset.

Mr. Shaffelburg reported having no disclosures. The study was funded by the CIRN SOS network, Canadian Institutes for Health Research, and a partnership with GlaxoSmithKline Biologicals. Some of the investigators were GSK employees or received grant funding from the company.